feat: native SSH delegation via tea.ExecProcess + Gruvbox palette

Phase A — Tamagosh-inspired redesign:
- Replace goroutine-based SSH (crypto/ssh) with tea.ExecProcess + native ssh binary
- Zero-lag SSH: native binary pegang TTY langsung, ga ada Go buffering
- Password auth via sshpass -e (SSHPASS env)
- Key auth via ssh -i <tmpfile> + SSH_ASKPASS for passphrase
- ControlMaster sockets for fast reconnect
- Add askpass subcommand for SSH_ASKPASS support
- Gruvbox Material Dark Hard palette for comfortable viewing
- Clean up old session messages (openSessionMsg, sessionOutputMsg, sessionDoneMsg)
- Remove 354-line session.go, replace with 150-line ssh.go

pkg/tui/tui.go

@@ -61,10 +61,11 @@ func (m *Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		m.Quit = true
 		return m, tea.Quit
 
-	case openSessionMsg:
-		tab := NewSessionTab(msg.host, m.dataDir)
-		cmd := m.tabs.Add(tab)
-		return m, cmd
+	case sshConnectToMsg:
+		return m, sshConnectCmd(msg.host, m.dataDir)
+
+	case sshExitMsg:
+		return m, nil
 
 	case openHostFormMsg:
 		var tab Tab
@@ -175,11 +176,6 @@ func (m *Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		}
 		return m, nil
 
-	case sessionDoneMsg:
-		if msg.err != nil {
-			m.Error = msg.err
-		}
-		return m, nil
 	}
 
 	cmd, err := m.tabs.Update(msg)